I'm wondering the same thing. I own a 07 335i that I purchased from a private party and the bmw dealership sold me a warranty thru "penske". Would the JB4 or AccessPort void my warranty even if i converted the car back to stock settings before warranty repair?

Dealers know when your car has been tuned. It stores shadow codes that log every time the ECU is flashed so it isn't hard for them to figure out that you are removing a tune every time you take it in. That said, most dealers don't care and just want the warranty work.

Ok thanks for the help guys. The main reason I am going to use it is simply for the race gas function. I go down to mid ohio a lot for photography and they have 110 octane race gas. I am simply going to ask my dealer if they will still do warranty work.

Don't ask the dealer to give you any sort of assurance in writing. They won't do it and you are just putting them in an impossible position by asking for that. The only way to be 100% safe warranty-wise is to leave the car alone. Once you make the decision to tune, you just go into the dealer like a boss and act real cool. You don't say shit, they won't say shit.

Ok thanks for the help guys. The main reason I am going to use it is simply for the race gas function. I go down to mid ohio a lot for photography and they have 110 octane race gas. I am simply going to ask my dealer if they will still do warranty work.

Should I have it in writing.

Thanks,

Why would you ask them to write you something. That writing just admits you're modding your car and allows them to void it.

I know you didn't ask but as an aside: the single most significant mod you can do to you car, bar none, is a limited slip differential. A 335i in stock form can't really put its power down effectively exiting turns. Putting a tune on the car just makes it worse. If you just zip from stoplight to stoplight or get your jollies by crushing Japanese hatchbacks full of sideways baseball cap-wearing teens, by all means tune it and enjoy. If you really like to drive, start by upgrading the driveline.